Mesa 7I37, Manual

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7I37 9
OPERATION
CONTROLLER REQUIREMENTS
PINOUT
The 7I37 is intended to operate with I/O cards that have 24 I/O bits and IO module
rack type connector pinouts (50 pin connector, all even pins grounded, +5 power on pin
49).
POLARITY
All controller interface pins are active low. This means a low controller output
indicates power applied to an opto-isolated input. A low output activates the corresponding
output MOSFET.
I/O VOLTAGES
The 7I37 accepts 3.3V or 5V signals and drives the FPGA card with 3.3V signals
so is compatible with 5V and 3.3V FPGA cards.
TIMING
MOSFET outputs turn on in ~3 uSec and off in ~7 uSec. Opto-isolated inputs turn
on on ~5 uSec and off in ~25 uSec.
INPUT CHARACTERISTICS
The opto-isolated inputs have 4.4K Ohm series resistors and reverse input
protection diodes across the opto-isolator LEDS. Input current an the maximum 24V input
is approximately 5mA. The isolated inputs will work with input voltages from 4 to 24V.
Note: The reverse input protection diodes are red LEDs. If you see a red LED
illuminated, this means you have reverse polarity DC or AC voltage applied to an
input.
OUTPUT CHARACTERISTICS
OUTPUT TRANSISTORS
The 7I37 outputs are small MOSFET power transistors with an on resistance of
approximately 0.25 Ohms, giving a saturation voltage of ~0.25V at full (1A) load. The
OBITx+ pins are the MOSFET drain connections and the OBITx- pins are the MOSFET
source connections. The MOSFETs have a built in drain-source diode.
INDUCTIVE LOADS
If the 7I37 outputs are used to switch inductive loads such as relays, some provision
for limiting the turn-off spike must be provided, such as a free wheeling diode across the
load or a R/C snubber.